In general, a sound converter is used as a concept including a speaker, etc. The speaker converts electrical energy into mechanical energy through a voice coil present in a void according to Fleming's left hand rule to thereby generate sound.
That is, when a current signal containing various frequencies is applied to the voice coil, the voice coil produces mechanical energy according to the intensity of the current and the magnitude of the frequency, causes vibration to a diaphragm attached to the voice coil, and ultimately generates a given magnitude of sound pressure which can be recognized by human ears.
A magnetic circuit of the speaker is designed in a yoke made of a ferrous metal element so that a magnetic flux can be interlinked perpendicularly to the voice coil present in the void by using a magnet (permanent magnet) and a top plate (or upper plate). The voice coil is adhered to the diaphragm to generate an electromotive force in the vertical direction according to an input signal, which vibrates the diaphragm adhered to and constrained by a frame to generate sound pressure.
The diaphragm is provided with various forms of waves to attain an excellent response and prevent a buckling phenomenon during the vertical vibration. The shape of the diaphragm is a factor which has the most significant effect on frequency characteristics.
FIG. 1 is a sectional view of a conventional sound converter.
As illustrated in FIG. 1, the typical sound converter includes a frame 1, a yoke 2 inserted into and mounted in the frame 1, an inner ring magnet 3 and an outer ring magnet 4 transferring the magnetic flux to the yoke 2 or receiving the magnetic flux from the yoke 2, an inner ring top plate 5 and an outer ring top plate 6 receiving the magnetic flux from the inner ring magnet 3 or the outer ring magnet 4 and transferring the magnetic flux perpendicularly to a voice coil 7, the voice coil 7 partially inserted into a void between the inner ring magnet 3 and the inner ring top plate 5 and the outer ring magnet 4 and the outer ring top plate 6, a diaphragm 8 having the voice coil 7 attached thereto to generate vibration according to the vertical motion of the voice coil 7, and a protector 10 having a sound emission hole 11 and protecting the diaphragm 8.
Additionally, a lead-out wire of the voice coil 7 is fixedly attached to the bottom surface of the diaphragm 8 by a bond, taken out through the lateral surface of the frame 1 or through a groove (not shown) formed in the frame 1, and soldered to a terminal 14 along the outer lateral surface of the frame 1.
In the conventional sound converter described above, an electric wire forming the voice coil 7 is made of a thick material so as to increase outputs, which increases the overall height of the voice coil 7. Accordingly, a space below the voice coil 7 should be so large that the voice coil 7 can be vibrated in the vertical direction to cause vibration to the diaphragm 8. To this end, if the voice coil 7 is made of a thick material to increase outputs, it needs to be positioned higher. For this, a seating portion of the diaphragm 8 should also be positioned higher. As a result, if the entire size of the sound converter does not increase, there is no sufficient vibration space for the upward dome-shaped diaphragm 8.
Moreover, even if the wire material of the coil is not thickened on account of mid frequency efficiency characteristics by weight, the amplitude of the diaphragm increases in a high-output mode, which requires efficient space utilization. Once the vibration space is obtained, the magnetic circuit space decreases, which degrades characteristics.
In another case, an aluminum alloy coil having a small specific gravity is used to improve mid frequency efficiency characteristics by its weight. This coil is often broken due to low strength, which results in low reliability.